JPH0412014A - Preparation of fine powdery silica - Google Patents

Abstract

PURPOSE:To prepare high quality fine powdery silica in a readily particle size- controllable state and in good productivity by spraying a water glass aqueous solution in the center of a high temperature combustion gas flow passing through a closed cylindrical oven with revolving. CONSTITUTION:A water glass aqueous solution is sprayed in the center of a high temperature combustion gas flow passing through a closed cylindrical oven with revolving to remove water and alkali from the water glass for providing the objective silica. In the method, the particles of the resultant fine silica are rarely fused with each other to produce bulky flocculates in a process in which the fine silica passes through a high temperature oven, but the phenomenon can be prevented by feeding a hydrocarbon into the high temperature combustion gas flow through a route different from the route of the water glass aqueous solution in an atomized state to prepare carbon black. The hydrocarbon for preparing the carbon black including styrene monomer and benzene.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing high quality fine powder silica from water glass raw materials with good operability.

[Conventional technology]

Conventional techniques for producing fine silica powder include flame hydrolysis of halogenated silicon compounds or silane compounds, Ostwald growth of colloidal silica obtained by ion exchange of sodium silicate, and neutralization of an aqueous solution of alkali silicate. Various methods are known, such as a reaction method and a method of wet hydrolyzing alkoxysilane.

[Problems to be Solved by the Invention] However, with these conventional techniques, there are difficulties in atomizing the formed silica and adjusting the particle size, and it is difficult to efficiently produce sized silica fine powder of 3μ or less. Met.

As a result of intensive research into a method for obtaining finely sized silica powder using a manufacturing method different from conventional techniques, the inventors dehydrated and dehydrated a water glass solution in high-temperature combustion gas under specific conditions. When alkali is used, the particle size is 0.01
The present invention was developed after confirming that high-grade silica fine powder was produced in the ~2μ range.

Therefore, the object of the present invention is to have a particle size of 0. The object of the present invention is to provide a method for producing high-quality fine powder silica in the fine particle range of 01 to 2 μm with easy particle size adjustment and high productivity.

[Means for Solving the Problems] A method for producing pulverized silica according to the present invention to achieve the above-mentioned object includes a water glass aqueous solution placed in the center of a high-temperature combustion gas flow circulating in a closed cylindrical furnace. The structural feature is that it dehydrates and dealkalizes by spraying it.

The high-temperature combustion gas flow flowing through the closed cylindrical furnace is formed by injecting fuel hydrocarbons into the furnace head together with an oxygen-containing air stream and completely combusting them. A connected carbon black generating furnace and a structured furnace of the same design can be effectively applied. At this time, by adopting a two-part swirling introduction method in which combustion gas is injected from two opposing directions in a tangential direction to the furnace axis, a flow of high-temperature combustion gas that circulates in the furnace can be formed.

As fuel hydrocarbons, fuel oils commonly used for producing carbon black, such as light oil, heavy oil, taleosote oil, and ethylene bottom oil, can be used, but propane, methane, etc. It is preferable to use a gaseous medium such as , butane. Further, the temperature inside the furnace needs to be maintained at a high temperature level of 1300° C. or higher at least at the position where the water glass aqueous solution is sprayed.

The water glass aqueous solution used as a raw material may be, for example, an inexpensive industrial water glass dissolved in water to an appropriate viscosity. Introduce into the furnace in a sprayed state.

Therefore, it is preferable to introduce the water glass aqueous solution through a spray nozzle installed in the center of the furnace head in the direction of the furnace axis.

The concentration of the water glass aqueous solution introduced into the furnace is desirably set to 20% by weight or less. When the concentration exceeds 20% by weight, the sprayed droplets become larger, the effect of crushing the primary droplets due to dehydration decreases, and the silicic acid content in the crushed secondary droplets increases, resulting in This will tend to increase the particle size of the silica obtained.

In addition, in order to spray uniform microdroplets of water glass aqueous solution into the furnace, a two-fluid type spray nozzle is used, and the fluid linear velocity (TVF: Tip Velocity) from the tip of the spray nozzle is used.
ty Factor) as 2000 ft/sec,
It is preferable to apply the above conditions. By providing such high-speed injection conditions, not only can solidification of sodium glass and silica at the tip of the burner be effectively prevented, but also the droplets of the sprayed water glass aqueous solution can be made even finer, resulting in uniform thermal decomposition. Moreover, the speed-up process proceeds smoothly, and the effect of pulverizing the produced silica to a submicron level is brought about.

The water glass aqueous solution sprayed into the furnace under the above conditions immediately comes into contact with the swirling high-temperature combustion gas flow, undergoes rapid thermal decomposition under strong shearing action, and causes a dealkalization reaction, resulting in particles of uniform particle size. Converts into fine powdered silica with high purity.

The generated fine powdered silica is water-cooled in the latter stage of the furnace, cooled to below its melting point, and then sent to a collection process and recovered.

In the above process, as the generated fine powder warping force flows through the high-temperature furnace, the particles may fuse together and form nodular aggregates, but this phenomenon is caused by the flow of high-temperature combustion gas. This can be effectively prevented by introducing hydrocarbons into the furnace in a sprayed state through a route different from that of the water glass aqueous solution to produce carbon black.

As the hydrocarbon for producing carbon black, for example, styrene monomer, Hensen, etc. are used. At this time, the spraying position of the hydrocarbon should be downstream from the spraying position of the water glass aqueous solution, since if it is introduced upstream from the spraying position of the water glass aqueous solution, carbon black may be dragged in during the generation of the warping force fine particle intermediate. Preferably, it is set in a furnace. In addition, the amount of carbon black coexisting is less than 50% by weight based on the amount of finely powdered silica produced, which is sufficient for the purpose of preventing fusion, and the generation of more than this is rather than the subsequent collection.
Makes operations such as removal complicated. Carbon black mixed in the collected fine powder silica can be removed by combustion and oxidation, and if necessary, it can be further purified by washing with mineral acid.

Furthermore, in order to further promote the dealkalization reaction of water glass during the thermal decomposition process, it is an effective means to spray an aqueous solution of an inorganic acid into the furnace.

Inorganic acids include hydrochloric acid, nitric acid, and gM, which are stable even in high-temperature atmospheres.
However, from the viewpoint of handling, it is preferable to use hydrochloric acid. For example, when using hydrochloric acid, C!
It has been recognized that the neutralization reaction between ions and Na ions proceeds easily at high temperatures, based on thermodynamic equilibrium constant calculations.

The position in the furnace where the inorganic acid aqueous solution is sprayed is preferably upstream of the introduction position of the water glass aqueous solution, and spraying from this position increases the degree of contact with the water glass droplets and causes them to be desorbed within a short time. Alkalinization is completed. If the aqueous inorganic acid solution is sprayed downstream from the aqueous water glass solution, the efficiency of the neutralization reaction will decrease and the effect of promoting dealkalization will be halved.

Further, as the method of spraying the aqueous inorganic acid solution, it is preferable to use an atomization method in order to improve mutual contact with the water glass droplets.

An equimolar amount of the inorganic acid aqueous solution is sufficient for the acid component to undergo a stoichiometric neutralization reaction with the alkali content in the water glass, but introducing a slightly excessive amount may promote dealkalization. This is suitable for achieving completeness. The most preferable amount of acid to be introduced is such that the molar ratio of the acid is at least 1.2 times the sodium content in the water glass.

The inorganic acid sprayed into the furnace under these conditions causes a neutralization reaction when it comes into contact with the thermally decomposed water glass droplets, thereby functioning to complete the dealkalization within a very short time.

Note that the type of closed cylindrical furnace used in the present invention may be either horizontal or vertical, but in the case of a vertical type, the glass material will be more stable due to the natural settling effect under gravity. Since adhesion to the furnace wall is effectively prevented, it is advantageous in terms of operability.

[For production]

According to the present invention, the water glass aqueous solution sprayed into the center of the high-temperature combustion gas flow that circulates in the closed cylindrical furnace immediately contacts and mixes with the combustion gas flow, and the shearing action of the swirling flow is activated. Due to the diffusion effect during dehydration, the primary droplets are pulverized uniformly and rapidly, and dealkalization progresses. Through this action, solid spherical fine powder silica with particle diameters in the range of 0.01 to 2 μm is continuously produced.

In addition, by adopting a configuration in which carbon black is generated and coexists in the high-temperature combustion gas during the process, it is possible to completely prevent the generated fine powder silica from adhering to each other, and it is always formed as a single true spherical particle. becomes possible.

Furthermore, injecting an aqueous solution of inorganic acid into the furnace accelerates the dealkalization reaction, significantly improving the purity of the generated warping force, and this function also raises the melting point of the silica fine particle intermediate, which reduces the fusion of silica fine particles with each other. This prevents the formation of secondary agglomerates and the adhesion of sodium glass to the furnace wall, which reduces operability.

The above effects work together to produce high quality fine powder silica with good productivity.

〔Example] Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 3 A combustion chamber (400 mm diameter
, length 300 mm) and a cylindrical reaction chamber (diameter 300 mm, length 1500 mm) connected coaxially with the horizontal closed cylindrical furnace. The reactor was installed along the axis of the reactor so as to be located 80 mm downstream from the head, and a cooling water injection nozzle for stopping the reaction was installed at the rear of the reaction chamber.

Using this furnace, a water glass aqueous solution was continuously sprayed into the center of a high-temperature combustion gas swirling flow introduced in a two-part swirling method to produce fine powdered silica. As the raw material for water glass,
Commercially available industrial water glass No. 3 having a composition of SiO□: 28 to 30% and Na, O: 9 to 10% was used (the same applies hereinafter).

Table 1 shows the characteristics and properties of each of the obtained fine powder silicas in comparison with the production conditions.

In addition, among the characteristics, the DCF method is applied to measure the particle size,
Disk rotation speed 1100Orp, sample liquid concentration 100mg
/100m1 sol, Sample injection amount 0. 5ml.

The test was carried out under the conditions of Hasofa-110.0ml. This measured value is in good agreement with the results obtained by scanning electron microscopy. Moreover, the Na content in silica is 1. Quantitative analysis was performed by atomic absorption spectrometry and fluorescent X-ray method.

From the results in Table 1, it can be seen that in Example 2, the water glass aqueous solution concentration was 5
In Example 3, the linear fluid velocity (TVF) for spraying the water glass aqueous solution was set as low as 1200 ft/sec, so the particle size of the produced silica tended to be larger in both cases than in Example 1. Approved.

Example 4 Using the same type of closed cylindrical furnace as in Example 1, 100 mm from the furnace head
Insert the water glass aqueous solution spray nozzle in the axial direction of the furnace so that the tip is located on the downstream side by 400 mm from the furnace head.
A hydrocarbon spray nozzle for carbon plaque generation was installed downstream of wIII.

Using this furnace, finely powdered silica was produced while generating carbon black under the production conditions shown in Table 1.

The obtained results are also listed in Table 1 in comparison with the production conditions. In this example, due to the coexistence of carbon black, the produced silica fine powder did not cause secondary aggregation due to mutual contact, and was recovered as a single perfectly spherical particle.

Examples 5 to 6 Using the same type of closed cylindrical furnace as in Example 1, 100 mm from the furnace head
A water glass aqueous solution nozzle is inserted in the axial direction of the furnace with the tip located on the +m downstream side, and separately from the furnace head.
An inorganic acid injection nozzle was installed at a position mm downstream.

Using this furnace, pulverized silica was produced while spraying HCj2 into the furnace under the production conditions shown in Table 1. The obtained results are also listed in Table 1 in comparison with the production conditions.

In these examples (Example 5.6) in which an inorganic acid was sprayed, the dealkalization of the water glass proceeded rapidly, and a single particle of finely powdered silica without secondary agglomerates was obtained.

Comparative Example A combustion chamber (diameter 400 m) equipped with one system of combustion burners and a spray nozzle for water glass aqueous solution in the axial direction of the furnace head.
m, length 300 mm), a cylindrical reaction chamber (diameter 300 mm, length 1500 mm) coaxially connected to the combustion chamber.
A closed cylindrical furnace was installed at the rear of the reaction chamber with cooling water spray holes for stopping the reaction.

Silica was produced using the furnace having the above structure and applying the production conditions shown in Table 1. As shown in Table 1, the obtained silica was a powder with a muco particle size of more than 2 μm and a low specific gravity in water, and some of the powder had a hollow balloon shape.

Fine powder silica having excellent purity and grain properties in the m range can be continuously produced with stable operability.

Therefore, it is useful as a method for producing fine silica powder, which is used as raw materials for fillers for metals, plastics, ceramics, etc., sintered filters, lightweight insulation materials, etc., as well as for filler applications such as semiconductor encapsulation and white pigments. .

Applicant: Tokai Carbon Co., Ltd. Agent: Patent Attorney Masaya Takahata

Claims (1)

[Claims] 1. Production of pulverized silica characterized by spraying a water glass aqueous solution into the center of a high-temperature combustion gas flow circulating in a closed cylindrical furnace for dehydration and dealkalization. Method. 2. The method for producing pulverized silica according to claim 1, wherein hydrocarbon is sprayed into the furnace downstream of the spraying position of the water glass aqueous solution to generate and coexist carbon black. 3. The method for producing finely divided silica according to claim 1, wherein an aqueous solution of an inorganic acid is sprayed into the furnace.